Aerial Spraying in Texas: Five Questions

The mayor of Dallas-Fort Worth, Texas, exercised his emergency powers last week and agreed to allow aerial mosquito spraying in response to the West Nile virus outbreak.

Photo courtesy of The Dallas Morning News

Residents were encouraged to minimize exposure by closing windows, keeping pets inside, and avoid being outside.

As an onlooker, I find myself asking questions about this news story. I no longer accept conventional health information without thinking through the issues. In the years prior to our unfortunate toxicology lesson, I would not have considered asking questions. Now I know better.

Here are five questions I have about the aerial spraying in Texas, along with carefully researched answers.

  1. What is in the pesticide?
    Answer: The product used for the aerial spraying consists of a compound known as Duet. Duet is manufactured by Clarke, a pesticide company based in Chicago. It is a combined mixture of sumithrin and prallethrin. Both of these are considered pyrethroids, derived from chrysanthemum flowers. This sounds innocent enough. However, according to the following fact sheet offered by the organization Beyond Pesticides:

    Almost all synthetic pyrethroid mosquito products use synergists like piperonyl butoxide (PBO), a petroleum distillate, which increases potency and compromises the body's ability to detoxify the pesticide. Petroleum distillates are carcinogenic and linked to birth defects and other illnesses.
    The information on pyrethroids says nothing about the inert ingredients of the product, which generally are not made public and contain numerous hazardous chemicals.
  2. Does this method of pest control work?
    Answer: I don't have a PhD in toxicology to know the answer to this question, so I asked toxicologist Dr. Jack Thrasher for his opinion:

    As has been published by the experts, spraying does not kill all of the adults nor does it kill the mosquito larvae. Larval-eating fish and draining of ponds are the most effective methods.
    Dr. Thrasher cites Beyond Pesticides' article West Nile Virus/Mosquito Management.

    Licensed pest control operator Gene Helmick-Richardson has a PhD in Entomology and actively opposes aerial spraying. In his blog titled Why Aerial Spraying for Mosquitos is a Terrible Plan, Richardson states, "I oppose any widespread spraying of adulticides for mosquito control because it simply doesn't work. It is a waste of time and resources when we should be focused on scientifically proven strategies to control this problem."

    The organization No Spray Nashville looked at 14 communities with mosquito control programs in place. Seven of them sprayed pesticides as a regular part of their programs. The other seven communities did not. The study, conducted in the years 2002 and 2003, found that:

    The communities that sprayed had an average of 1.37 people with West Nile virus per 100,000. The communities that didn't spray had 1.19 people with West Nile virus per 100,000. The results show no significant difference in West Nile virus rates between communities that spray and those that don't.
  3. What are the environmental implications?
    Answer: There are more questions than answers. Intuitively we know that if our goal is to kill the mosquitoes that carry the West Nile virus, surely we risk killing beneficial insects as well. If we reduce the number of beneficial insects, don't we risk increasing the bad ones? Clarke, the manufacturer of Duet, admits that the spray is toxic to honeybees. We know that honeybees are essential for the pollination of many fruits and vegetables. (The local CBS affiliate's story West Nile Spraying Could Affect North Texas Bees discusses this in detail.)

    Texas A&M is attempting to track the environmental impact by offering a survey to local residents, stating:

    The survey is designed to be completed approximately one week after completion of aerial spraying. This delay is necessary because we would like you to have enough time to assess impact over several days, since insect populations are naturally variable from day to day.
    If we used non-toxic methods for mosquito control, would we need such a survey?
  4. What are the health implications?
    Answer: Pyrethroids are known endocrine-disrupting chemicals (EDCs), a class of chemicals that researchers have recently found can mix up critical hormonal signals even in extremely small amounts. This defies the traditional toxicological premise that more exposure means higher risk. The American Medical Association is already calling for reduced exposure to endocrine-disrupting chemicals. A study released this spring by the Endocrine Society concludes:

    Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities.
    Many of these effects wouldn't be noticed for years, even decades, which makes the benefit/risk evaluation difficult if not impossible.
  5. Are there alternatives to aerial spraying?
    Answer: There are a number of options. According to Dr. Gene Helmick-Richardson (article cited above):

    It starts with controlling the breeding sites. All stagnant water pools in the area should be located and either drained, treated with larvacides, or populated with mosquito fish. Educational programs like NY's Fight the Bite program and similar outreach programs have proven effective in preventing exposure and limiting populations of mosquitoes. The manpower and expense involved in such programs, which include stricter code enforcement, free distribution of larvacides, and even door-to-door visits by volunteers or trained staff are not very high when compared to the cost of aerial pesticide application. And besides, they actually work.
    Beyond Pesticides provides an outstanding fact sheet titled Backyard Mosquito Management, offering numerous non-toxic suggestions for mosquito control. Don't miss these options if you're fighting your own mosquito battle this summer!
Concluding thoughts:
Even without convincing research, I would oppose aerial spraying. Planes spraying small doses of hazardous chemicals above my home violates my freedom to choose what is best for my family. My home's ecosystem, our pets, and our children are all at risk without my permission.

A practice I'm willing to question.